1. Field of the Invention
The present invention relates to a self-sealing gravity assisted pit lid mounting system for an access lid to a subsurface chamber for servicing aircraft.
2. Description of the Prior Art
At modern aircraft terminals the servicing of aircraft on the ground is frequently performed using subsurface pits, which are often prefabricated structures. Such aircraft servicing pits are installed at aircraft docking, fueling, and loading areas beneath the surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits forming a subsurface chamber are typically constructed of fiberglass, steel, concrete, or aluminum. These pits are typically fabricated as complete enclosures with surrounding walls, a floor, and an access lid at the top seated within a frame disposed at the mouth of the prefabricated pit. When the lid is closed it lies substantially flush with the surface of the tarmac. Such pits are installed below the surface of loading and refueling aprons at aircraft terminals, remote parking locations, and aircraft maintenance bases.
The purpose of such pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to the aircraft while it is in the docking area, the provision of air for cooling the aircraft interior, the provision of pressurized air for starting the aircraft engines, and for other aircraft support activities on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts, and other vehicles which are otherwise necessarily present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate.
The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with greater efficiency at a central location, as contrasted with mobile generating or supply vehicles.
The pits located below the aircraft terminal area house valves, junction boxes, cooling air terminations, and other terminal equipment that is temporarily connected to an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from them through hatches therein and are coupled to a docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, electrical power, and other ground support functions.
The pits are constructed with either hinged or totally removable lids that can be moved between open positions allowing access to the pits and closed positions which are flush with the surfaces of the docking, loading, or refueling areas across which aircraft travel and beneath which the pits are mounted. To ensure that the pit lids remain flush with the surrounding surfaces it is desirable to employ a latching mechanism.
The pit access lids in such aircraft servicing pits are extremely heavy, since they must be able to withstand the weight of the wheels of a large aircraft traveling thereacross. Therefore, it is often very difficult to open such access lids without assistance.
Conventional pit access lid mounting systems sometimes employ lift assisted springs that are interconnected to the pit lid in such a way as to act in opposition to gravitational force on the lid, thereby aiding the service personnel in opening of the lid. One such spring-loaded mechanism is described, for example, in U.S. Pat. No. 5,950,368. As illustrated in that prior patent, the pit lid is mounted relative to the mouth of the pit in such a way as to be movable from an open position completely clear of any contact with the mouth of the pit, and a closed position in which a gasket about the periphery of the pit lid provides a liquid-tight seal completely about the perimeter of the mouth opening to the pit. This ensures that rain and melting snow cannot wash dirt and other debris down into the pit.
Spring assisted pit lid mounting systems have certain disadvantages, however. With age and exposure to the elements the springs can rust and break. Consequently, in some applications a gravity assisted pit lid mounting system is preferable. One such gravity assisted system that employees counterweights that are coupled to the pit lid through a system of meshed gears has been used very successfully for many years. This system is described in U.S. Pat. No. 4,467,932. However, one disadvantage of existing gravity assisted pit mounting systems is that it has not heretofore been possible to provide a liquid-tight seal for lids mounted in this manner about their entire periphery. As a consequence, there can be leakage into the pits from rain and melting snow that seeps into the mouth of the pit at the hinge opening. This is because the mounting systems for conventional gravity assisted pit lids have not heretofore provided a complete seal at the top of the pit.
The present invention provides a unique pit access lid mounting system that not only aids the user in opening the pit lid using a system of counterweights, but also a system that allows a liquid-tight seal to be established about the complete perimeter of the pit lid when the pit lid is rotated about its hinge axis to its closed position, and which provides a complete watertight seal at the top of the pit. Thus, the system of the present invention enables the use of counterweights mounted on a pair of counterweighted arms and coupled to move in counterrotation relative to a hinged pit lid and also provides such a system with a complete watertight seal at the mouth of the opening to the subsurface chamber of the pit.
One primary object of the present invention is to provide a subsurface aircraft servicing pit for use in servicing aircraft while they are on the ground which avoids the use of springs to assist the user in opening the pit lid, but which still provides the pit lid with a continuous, watertight seal about its peripheral edge when it is seated atop the mouth of the buried pit. By employing these features the disadvantages associated with the use of springs to offset the weight of the lid are avoided, but while providing a pit lid hinging arrangement that does not have a break in the watertight seal at the pit lid hinge axis. This latter feature is a disadvantage of conventional counterweighted pit lid systems.
A related object of the invention is to provide an improved subsurface aircraft servicing pit of the type used with conventional counterweighted pit lid assist systems that will accommodate an improved mounting mechanism according to the invention without changing the structure of the pit itself. Rather, the same pit that is utilized to accommodate the gearbox of a conventional gravity assisted pit lid lift mechanism is employed in the system of the present invention, but is provided with a lid seating rim assembly at the mouth of the pit with flanges that extend over the gearbox areas of the pit and seal it in watertight fashion.
To permit the pit lid to be both gravity assisted by counterweights and sealed throughout at its top, the pit lid lifting arms are reconfigured from conventional designs. Specifically, they are constructed with central U-shaped intermediate portions between their ends so as to permit them to be hinged underneath the pit rim, rather than set into upwardly facing, exposed pockets in the frame surrounding the pit lid.
A further object of the invention is to provide a counterweighted pit lid that avoids damage to the structure of the pit by the counterweights if the lid is thrown open in a violent manner. In conventional counterweighted pits it is possible for the counterweights to strike the upright wall of the pit at which the meshed counterweight gears are located with a very large force. The impact can damage the structure of the pit, if the pit lid is thrown or blown open. This can occur either due to inattention on the part of the servicing personnel, or due to the force of wind or exhaust blasts from jet airplanes in the vicinity. In either case, the structural integrity of the pit is compromised if the counterweights severely impact the wall of the pit.
Damage to the pit of the present invention is prevented by interposing a shock absorber between one or both of the counterweight arms and the wall of the pit. The shock absorbers dampen the impact of the counterweights against the pit wall, and may indeed prevent any contact at all.
In one broad aspect the present invention may be considered to be an improvement in an aircraft servicing pit defining a subsurface chamber below a surface across which aircraft travel when not airborne. The pit has at least one upright wall and an upwardly opening mouth formed by a continuous rim that has an enclosing perimeter that circumscribes and defines the mouth. A pit lid having an upper surface and an undersurface is disposed atop the mouth and hinged for rotation relative to the pit about a lid hinge axis to an open position completely free from the rim and alternatively to a closed position sealing the mouth and seated throughout the entire perimeter of the rim.
The improvement of the invention is comprised of a pair of pit lid arms supporting the pit and having distal ends that are secured to the undersurface of the pit lid at a spaced distance of separation from the lid hinge axis and proximal ends that are rotatably joined to the pit at the lid hinge axis beyond the perimeter of the rim and beneath the surface across which aircraft travel. At least one counterweight arm hinge pin is located beyond the perimeter of the rim and below the level of the surface across which aircraft travel. A pair of counterweight supporting arms each having a distal end bearing a counterweight and an opposite proximal end rotatably joined to the pit at the counterweight arm hinge pin are provided. At least one pit lid gear is rigidly secured to the proximal end of at least one of the pit lid arms. At least one counterweight gear is rigidly secured to the proximal end of at least one of the counterweight arms. The pit lid gear and the counterweight gear are meshed together. In this way the distal ends of the counterweight arms are raised as the pit lid is moved to the open position and lowered as the pit lid is moved to the closed position.
The lid supporting arms preferably both have a U-shaped configuration between their proximal and distal ends. Further, a resilient sealing loop of flexible material is disposed about the pit lid so as to reside in liquid-tight sealing engagement throughout the perimeter of the rim when the pit lid is in the closed position. The sealing loop is preferably formed of a rubber gasket and the pit lid is preferably provided with a radially directed gasket seating channel extending about its entire perimeter. The rubber gasket is entrapped in the seating channel. Preferably also, a shock absorber is interposed between at least one of the counterweight arms and the upright pit wall.
In another broad aspect the invention may be considered to be an improvement in an aircraft servicing pit buried below a surface across which aircraft travel and defining a subsurface chamber. The pit has at least one upright wall at the top of which a pit access lid capable of withstanding the weight of the tires of aircraft traveling thereacross is mounted on a lid hinge for rotation about a horizontal pit access lid axis. The aircraft servicing pit includes a gravity operated balancing mechanism having at least one counterweight located in the subsurface chamber and mounted relative to the wall by at least one counterweight arm and at least one counterweight hinge means for rotation about a counterweight axis parallel to the lid axis. At least one pair of meshed gears are provided for joining the lid and the counterweight arms for movement in counterrotation together. The counterweight or counterweights exert a rotational moment opposed to and less than the moment resulting from the weight of the lid.
According to the improvement of the invention a pair of pit lid lifting arms having distal ends fastened to the lid at locations remote from the lid axis and proximal ends hinged relative to the pit at the lid axis are rigidly secured at the lid axis to one of the meshed gears in the pair of gears. The counterweight arm is rigidly secured to the other of the gears in the pair of gears. Both the lid axis and the counterweight axis are located beneath the surface across which aircraft travel. The pit access lid is rotatable about the pit access lid axis in counterrotation with the counterweight arm between a raised, open position permitting access to the subsurface chamber and a lowered, closed position in liquid-tight sealed relation atop the subsurface chamber.
In still another aspect the invention may be considered to be an aircraft servicing pit comprising: a pit buried beneath a surface across which aircraft travel and having a mouth opening at its upper end and at least one upright wall therewithin and defining within its structure a subsurface chamber for use in servicing aircraft, an access lid, at least one hinge, and a counterweight means. The access lid is able to withstand the weight of the tires of an aircraft traveling thereacross and is located at the mouth of the pit. At least one hinge mounts the lid to the pit at the mouth thereof so that the lid is movable in rotation about a lid axis to an open position completely clear of the mouth and a closed position completely sealing the mouth throughout its perimeter with a liquid-tight seal therebetween. A counterweight means is mounted within the subsurface chamber for rotatable movement in an arcuate path relative to the upright pit wall about a counterweight axis parallel to the lid axis. A coupling means rigidly links the counterweight means to move in counterrotation with the lid
The invention may be described with greater clarity and particularity by reference to the accompanying drawings.